Lithium batteries have been the subject of numerous studies, because of their multiple uses and their performance characteristics. Their future, however, is in jeopardy because of the limited natural availability of lithium.
Some of the properties of sodium are similar to those of lithium, and its use as an alternative solution in batteries has been studied.
It is known practice to use sodium in Na/S batteries which operate at high temperature for storage on the megawatt or MW scale. Also known are Na/NiCl2 systems for electric vehicles. These two types of batteries, however, operate only in a high-temperature range (of the order of 270-300 °C.), where they benefit from the high conductivity of β-alumina ceramics.
Other attempts have been made to produce batteries where the negative is electrode is a sodium metal electrode and the positive electrode is a sodium ion insertion material. Examples include liquid-electrolyte batteries in which the positive electrode is composed of TiS2 or a transition metal oxide having a high oxidation potential, such as NaxMO2, for example, M being Mn or Co. Also included are batteries Which operate by circulation of sodium ions between a negative electrode, composed of carbon, and a positive electrode, composed of a phosphate of sodium and a transition metal (US-2002-0192553). However, the capacity of batteries which operate by circulation of sodium ions in the electrolyte, with a carbon negative electrode, is unstable over time, and falls rapidly in the course of successive cycles.
The compound Na2Ti3O7, and its capacity for reversible insertion of lithium ions, without detriment to the crystallographic structure, are known [K. Chiba, et al., Solid State Ionics, 178 (2008)1725-1730]. It is noted, however, that the reversible capacity of the Na2Ti3O7 material is significantly lower than that of the lithium-containing material, Li2,Ti3O7, having the same structure.